Description of the Prior Art
U.S. Pat. No. 3,036,134 to Mattox discloses the conversion of methanol to a reaction product containing water and dimethyl ether in the presence of, as a catalyst, a crystalline aluminosilicate.
Copending application Ser. No. 387,223, filed Aug. 9, 1973, (now U.S. Pat. 3,894,107) discloses the conversion of alcohols and other similarly substituted simple hydrocarbon compounds to a reaction product containing water and highly aromatic, gasoline boilingrange hydrocarbons, by contacting such reactant with a crystalline aluminosilicate having a silica to alumina ratio of at least about 12 and a constraint index, as there defined, of about 1 to 12.
Copending application Ser. No. 387,222, filed Aug. 9, 1973 (now U.S. Pat. 3,894,106), discloses the conversion of ethers to a reaction product containing water and gasoline hydrocarbons by contacting such with a similarly defined catalyst.
The applicable class of catalysts is exemplified by ZSM-5, ZSM-11, ZSM-12, ZSM-21, and TEA Mordenite.
U.S. Pat. No. 3,702,886 issued Nov. 14, 1972 to Argauer et al. discloses ZSM-5 zeolite catalyst.
U.S. Pat. No. 3,709,979 issued Jan. 9, 1973 to Chu discloses ZSM-11 zeolite catalyst.
West German Auslegeschrift No. 2,213,109 discloses ZSM-12 catalyst.
Copending application Ser. No. 358,192, filed May 7, 1973 (now abandoned), discloses ZSM-21 catalyst.
Copending application Ser. No. 130,442, filed Apr. 1, 1971 (now abandoned), discloses TEA mordenite.
Although the above-described conversions perform exceptionally well and are unusually effective at converting various non-gasoline organic chemicals to high quality gasoline, it has been found that these conversions are exothermic to varying degrees depending on the particular reactant. For example, the amount of heat generated in the conversion of the lower alcohols to hydrocarbon product may be estimated to be in the ranges shown:
______________________________________ Heat Produced, BTU per lb. of Alcohol Reactant Hydrocarbon Product ______________________________________ Methanol 1300-2000 Ethanol 280-620 Propanol 20-360 ______________________________________
While it is desirable that a reaction be exothermic, since this obviates the need for an external source of heat to drive the reaction, large heat generation loads can require substantial investment in complex reactors with extensive internal cooling means, thereby detracting from the overall economic efficiency of the process. It can be seen from the above table that the conversion of methanol, and to a lesser degree of ethanol, could be considered excessively exothermic in this regard. Furthermore, because of the inherent character and efficiency of the above described crystalline aluminosilicate zeolite catalysts, the reaction of methanol, and to a lesser degree of ethanol, tend to be self-accelerating, thereby creating excessively hot local regions, where the reaction tends to go to completion, in the catalyst bed. Thus, the simple expedient of conducting the reaction partially in a first catalyst bed and completing it in a second catalyst bed is not available to facilitate heat removal. Additionally, it is generally good engineering practice to conduct reactant conversions at elevated pressures to more effectively utilize the reactor volume and process recovery of the reactor effluent. With a methanol charge, however, elevated pressures tend to produce increased quantities of 1, 2, 4, 5 tetramethylbenzene (durene). This product is believed to result at least in part from the mixing and reaction of yet-unconverted methanol with aromatic hydrocarbon products. In some situation, for example, when it is desired to utilize the conversion products as gasoline or to manufacture benzene, toluene and xylenes, durene is an undesirable by-product.